This invention relates to an improved method and device for removing liquid and the like from a moving surface, such as in process lines which manufacture or treat continuous flat rolled products or strip.
Many methods and devices have been employed to remove liquids and particulate matter from the surfaces of continuous sheet or strip and other moving surfaces including those based on vacuum and those based on jets or curtains of high velocity gas, commonly called air knives. Such devices and methods have been used in rolling mills to remove lubricant and/or coolant from the sheet or strip being rolled and also in other process lines, such as in painting, anodizing, or plating lines to remove liquids.
Each of the prior liquid removal devices has both advantages and disadvantages. For example, vacuum devices can effectively remove the liquid from a moving sheet or strip under conditions where the liquid is uniformly distributed over the sheet or strip surface, provided that the speed of the sheet or strip is slow enough and the volume of induced air is large enough to ensure entrainment of all the free liquid and the complete evaporation of any moisture remaining on the sheet or strip. However, large surges of liquid on the sheet or strip tend to overwhelm vacuum systems so that the liquid is not completely removed. Air knives, which are based on high velocity jets or a curtain of gas, can be very effective liquid removing devices, even with large surges of liquid, but these devices have a tendency to blow the liquid removed from the sheet or strip into the surrounding environment where it can impinge or condense upon associated equipment and ultimately drip back upon the surface of the strip or sheet, thereby requiring further treatment.
Liquid removal devices which employ both vacuum units and air knives such as those described in U.S. Pat. No. 3,192,752 have been somewhat more successful, particularly in rolling mill operations, but these, too, also seem to provide less than adequate removal of liquid from the moving sheet or strip, particularly at the high speeds commonly found in modern rolling mills, e.g., 3000-5000 feet per minute (914-1524 meters per min.). Even though vacuum units are employed, a fine mist frequently builds up in the immediate vicinity of the rolling mill and liquid which redeposits or condenses on strip may require further treatment of the sheet or strip.
In the treatment of aluminum and aluminum alloy sheet or strip wherein the liquid on the aluminum sheet or strip is water or a water-based fluid, additional problems are encountered because water rapidly reacts with fresh aluminum surfaces to form a white oxide product commonly termed "water stain". Water stain formation is particularly noticeable in the rolling of aluminum with waterbased lubricants if all of the aqueous phase of the lubricant is not removed from the strip before coiling.
The modern, high speed rolling mills presently used to cold roll aluminum and aluminum alloys have the capability of speeds up to 5000 feet per minute (1524 meters per minute) or more. At speeds of this magnitude, the effectiveness of the liquid removal device becomes most important because frequently the maximum speed at which the rolling mill may be effectively operated is severely reduced by the inability of the liquid removal device to keep the surface of the strip or sheet free from aqueous phase after rolling.
It is against this background that the present invention was developed.